JP6881382B2 - All solid state battery - Google Patents

Description

The present disclosure relates to an all-solid-state battery.

With the rapid spread of information-related devices such as personal computers, video cameras and mobile phones, and communication devices in recent years, the development of batteries used as their power sources has been emphasized. In addition, the automobile industry and the like are also developing high-output and high-capacity batteries for electric vehicles or hybrid vehicles.
Among all-solid-state batteries, lithium-ion all-solid-state batteries have a high energy density because they utilize a battery reaction that involves the movement of lithium ions, and an electrolyte solution containing an organic solvent as an electrolyte interposed between the positive electrode and the negative electrode. Attention is being paid to the fact that a solid electrolyte is used instead of.

Since the active material made of Si-based material has a large theoretical capacity per volume, a lithium ion all-solid-state battery using Si-based material as a negative electrode has been proposed.
Patent Documents 1 to 3 disclose an all-solid-state battery using Si as a negative electrode active material.
Patent Document 4 discloses the porosity of the solid electrolyte layer for the purpose of improving the discharge capacity of the non-aqueous electrolyte battery.
Patent Document 5 discloses that the voids in the negative electrode for an all-solid-state battery are gaps surrounded by a sulfide solid electrolyte and / or a negative electrode active material, and the void ratio in the negative electrode is 5 to 30%. ing. In Patent Document 5, a matrix of Si and a carbon material is used as a negative electrode active material. Therefore, there is no description about voids in the solid electrolyte contained in the negative electrode.

Japanese Unexamined Patent Publication No. 2014-192093 Japanese Unexamined Patent Publication No. 2013-06916 Japanese Unexamined Patent Publication No. 2017-059534 Japanese Unexamined Patent Publication No. 2013-016280 JP-A-2017-054720

In the case of an all-solid-state battery using a negative electrode layer containing a Si-based material as the negative electrode active material, the volume expansion rate of the negative electrode active material during charging is large, so a jig for suppressing the expansion of the battery is required, and the battery There is a problem that the energy density of the battery decreases.
Further, if only increasing the voids in the negative electrode layer in order to suppress the expansion of the battery, it may be difficult to secure the contact property between the negative electrode active material and the solid electrolyte, so that the battery resistance may increase. There is.
In view of the above circumstances, it is an object of the present disclosure to provide an all-solid-state battery having a negative electrode layer containing a Si-based material as a negative electrode active material and having a high energy density.

The present disclosure is an all-solid-state battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer arranged between the positive electrode layer and the negative electrode layer.
The negative electrode layer contains a negative electrode active material containing at least one Si-based material selected from the group consisting of Si and a Si alloy, and a solid electrolyte containing a sulfide-based solid electrolyte.
In the negative electrode layer, there is an inter-electrolyte void surrounded by the solid electrolyte, at least in a region composed of the solid electrolyte.
When the total volume of the negative electrode layer is 100% by volume, the porosity occupied by the interelectrolyte voids in the negative electrode layer is 3.4% by volume or more and 29.6% by volume or less. Provide batteries.

In the all-solid-state battery of the present disclosure, the negative electrode layer may further contain fibrous carbon as a conductive material.

In the all-solid-state battery of the present disclosure, when the total volume of the negative electrode layer is 100% by volume, the porosity occupied by all the voids existing in the negative electrode layer of the negative electrode layer is 5% by volume or more and 38% by volume. It may be as follows.

In the all-solid-state battery of the present disclosure, when the total volume of the region composed of the solid electrolyte in the negative electrode layer is 100% by volume, the porosity occupied by the space between the electrolytes in the region is 40% by volume or more. It may be 80% by volume or less.

According to the present disclosure, an all-solid-state battery having a negative electrode layer containing a Si-based material as a negative electrode active material and having a high energy density is provided.

It is sectional drawing which shows an example of the all-solid-state battery of this disclosure. It is a schematic diagram which shows an example of the negative electrode layer used in this disclosure.

The present disclosure is an all-solid-state battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer arranged between the positive electrode layer and the negative electrode layer.
The negative electrode layer contains a negative electrode active material containing at least one Si-based material selected from the group consisting of Si and a Si alloy, and a solid electrolyte containing a sulfide-based solid electrolyte.
In the negative electrode layer, there is an inter-electrolyte void surrounded by the solid electrolyte, at least in a region composed of the solid electrolyte.
When the total volume of the negative electrode layer is 100% by volume, the porosity occupied by the interelectrolyte voids in the negative electrode layer is 3.4% by volume or more and 29.6% by volume or less. Provide batteries.

While Si has a higher volume than the carbon material, the volume change when it reacts with Li is very large, and the volume expands 3 to 4 times.
A battery using a solid electrolyte conducts Li by a solid electrolyte (SE) provided around the active material.
If the voids in the negative electrode layer are reduced as much as possible in order to maintain a sufficient contact area between the solid electrolyte and the negative electrode active material, a space for the expanded Si to escape during volume expansion due to the insertion of Li into Si when Si reacts with Li. There is no.
Since the pressure on the restraining jig increases due to the swelling of the negative electrode layer, if a restraining jig with sufficient strength is used, the wasted volume other than the battery when packed increases, and the energy of the battery as a whole system The density does not increase.
On the other hand, if the void ratio in the negative electrode layer is increased, the increase in pressure can be suppressed, but the contact area between the solid electrolyte and the negative electrode active material is small, and the resistance value of the battery when the battery is discharged (the active material shrinks) becomes high. It ends up.
Therefore, there is a problem that it is difficult to both relax the restraining pressure of the battery and reduce the resistance value of the battery.

The researchers placed solid electrolytes around the negative electrode active material without any gaps without changing the total porosity of the negative electrode layer, and increased the voids (interelectrolyte voids) in the region composed of the solid electrolytes. I let you. This makes it easier to absorb the expansion of the negative electrode active material when the battery is charged. As a result, the resistance value of the battery could be lowered by suppressing the increase in the pressure of the battery and improving the contact property at the interface between the negative electrode active material and the solid electrolyte. That is, it was possible to suppress the increase in the pressure of the battery and to reduce the resistance value of the battery at the same time.
Simply providing voids in the negative electrode layer reduces the interface between the negative electrode active material and the solid electrolyte, thus increasing the resistance of the battery. On the other hand, by arranging a solid electrolyte around the negative electrode active material and increasing the voids in the region composed of the solid electrolyte, the increase in battery resistance is suppressed and the restraining pressure by the jig when charging the battery is suppressed. It is presumed that the increase in the amount can be suppressed.
According to the present disclosure, expansion of the negative electrode active material during charging of the battery can be suppressed by providing voids (voids between electrolytes) in the region composed of the solid electrolyte in the negative electrode layer. Therefore, the number of jigs for suppressing the expansion of the battery can be reduced, and the decrease in the energy density of the battery can be suppressed.
Further, the space between the electrolytes is provided in the region surrounded by the solid electrolyte in the region composed of the solid electrolyte in the negative electrode layer. Therefore, since the contact property at the interface between the negative electrode active material and the solid electrolyte can be sufficiently ensured, an increase in battery resistance can be suppressed.

In the present disclosure, the "region composed of solid electrolytes in the negative electrode layer" (hereinafter, may be referred to as a solid electrolyte region) includes solid electrolytes, and the solid electrolytes come into contact with each other and are connected to each other. It is an area that has become. Specifically, when the negative electrode layer contains a negative electrode active material, a solid electrolyte, and other materials, the solid electrolyte region is a region in the negative electrode layer excluding the region where the negative electrode active material and other materials are present. At least one solid electrolyte region exists in the negative electrode layer, and a plurality of solid electrolyte regions may be present.

In the present disclosure, the "electrolyte gap" is a void existing in the region surrounded by the solid electrolyte in the region composed of the solid electrolyte in the negative electrode layer. Specifically, it is a void generated by contacting particles of solid electrolytes in the negative electrode layer, and is generated by contact between the solid electrolyte and a material constituting the negative electrode layer such as a negative electrode active material other than the solid electrolyte. It is a void excluding the void between the negative electrode active material and the solid electrolyte and the void between the active materials generated by the contact between the particles of the negative electrode active material.

FIG. 1 is a schematic cross-sectional view showing an example of the all-solid-state battery of the present disclosure.
As shown in FIG. 1, the all-solid-state battery 100 is located between a positive electrode 16 including a positive electrode layer 12 and a positive electrode current collector 14, a negative electrode 17 including a negative electrode layer 13 and a negative electrode current collector 15, and between the positive electrode 16 and the negative electrode 17. The solid electrolyte layer 11 is arranged in.

FIG. 2 is a schematic view showing an example of the negative electrode layer used in the present disclosure.
As shown in FIG. 2, the solid electrolyte particles 21 and the negative electrode active material particles 22 are present in the negative electrode layer 13. The region shown by the broken line in FIG. 2 is the solid electrolyte region 23. Therefore, the solid electrolyte region 23 is a region in the negative electrode layer 13 that does not contain the negative electrode active material particles 22. In the solid electrolyte region 23, there is an inter-electrolyte void 24 surrounded only by the solid electrolyte particles 21. Further, the negative electrode active material-solid electrolyte gap 25 surrounded by the solid electrolyte particles 21 and the negative electrode active material particles 22 may exist in the negative electrode layer 13.

The negative electrode has at least a negative electrode layer, and if necessary, further includes a negative electrode current collector.
The negative electrode layer contains at least a sulfide-based solid electrolyte and a negative electrode active material, and if necessary, contains a conductive material and a binder.
Examples of the negative electrode active material include at least one Si-based material selected from the group consisting of Si and Si alloys. Examples of the Si alloy include alloys with metals such as Li, and other alloys may be alloys with at least one metal selected from the group consisting of Sn, Ge, and Al.
Si reacts with a metal such as Li to form an amorphous alloy by the initial charge performed after assembling the all-solid-state battery. Then, the alloyed portion remains amorphous even after metal ions such as lithium ions are released by electric discharge. Therefore, in the present disclosure, the negative electrode layer using Si includes a state in which Si is amorphous alloyed.
The shape of the negative electrode active material is not particularly limited, and examples thereof include a particle shape and a plate shape.
The average particle size (median diameter D50 of the volume distribution) of the negative electrode active material particles may be 10 μm or less, preferably 5 μm or less, and more preferably 3 μm or less.
In the present disclosure, the average particle size of the particles is a value measured by laser diffraction / scattering type particle size distribution measurement. Further, in the present disclosure, the median diameter is a diameter at which the cumulative volume of particles is half (50%) of the total number of particles when the particles are arranged in ascending order.
The content of the negative electrode active material in the negative electrode layer is not particularly limited, but may be, for example, 20% by volume to 90% by volume when the total volume of the negative electrode layer is 100% by volume.

The solid electrolyte used for the negative electrode layer may be at least a sulfide-based solid electrolyte.
Examples of the sulfide-based solid electrolyte include Li ₂ S-SiS ₂ , LiI-Li ₂ S-SiS ₂ , LiI-Li ₂ S-P ₂ S ₅ , LiI-Li ₂ S-P ₂ O ₅ , LiI-. _{Li 3 PO 4 -P 2 S 5} , LiI-Li 2 O-Li 2 S-P 2 S 5, LiBr-LiI-Li 2 S-P 2 S 5, Li 2 S-P 2 S 5 -GeS 2, Examples thereof include _{Li 2} SP ₂ S _5.
Specifically, Li ₁₀ GeP ₂ S ₁₂ , Li ₈ P ₂ S ₉ , 15LiBr ・ 10LiI ・ 75 (0.75Li ₂ S ・ 0.25P ₂ S ₅ ), 70 (0.06Li ₂ O ・ 0.69Li) ₂ S ・ 0.25P ₂ S ₅ ) ・ 30LiI and the like can be mentioned. As the solid electrolyte, one kind alone or two or more kinds can be used.
Further, the solid electrolyte may be any of a solid electrolyte crystal, an amorphous solid electrolyte, and a solid electrolyte glass ceramics.
The shape of the solid electrolyte is not particularly limited, and examples thereof include a particle shape and a plate shape, and may be preferably a particle shape.
The content of the solid electrolyte in the negative electrode layer is not particularly limited, but may be, for example, 10% by volume to 80% by volume when the total volume of the negative electrode layer is 100% by volume.

[Porosity]
In the negative electrode layer in the present disclosure, when there are gaps between electrolytes surrounded by the solid electrolyte in at least a region composed of the solid electrolyte, and the total volume of the negative electrode layer is 100% by volume, the negative electrode layer The void ratio occupied by the inter-electrolyte voids (hereinafter, may be referred to as the inter-electrolyte void ratio in the negative electrode layer) is 3.4% by volume or more and 29.6% by volume or less, and the effect of lowering the battery resistance and the lowering of the restraining pressure. From the viewpoint of improving the balance of effects, the lower limit value may be preferably 8.3% by volume or more.
Further, when the total volume of the negative electrode layer is 100% by volume, the porosity occupied by all the voids existing in the negative electrode layer of the negative electrode layer (hereinafter, may be referred to as the total porosity in the negative electrode layer) is 5. It may be 5% by volume or more and 38% by volume or less, and preferably, the lower limit value may be 15% by volume or more from the viewpoint of improving the balance between the effect of lowering the battery resistance and the effect of lowering the restraining pressure. The "all voids existing in the negative electrode layer" are not only the voids between the electrolytes but also the voids other than the voids between the electrolytes and the voids including other voids such as the voids between the active material and the solid electrolyte. is there.
Further, when the total volume of the region composed of the solid electrolyte contained in the negative electrode layer is 100% by volume, the porosity occupied by the interelectrolyte voids in the region (hereinafter referred to as the porosity between the electrolytes in the solid electrolyte region). ) May be 40% by volume or more and 80% by volume or less, and the lower limit is preferably 52% by volume or more from the viewpoint of improving the balance between the effect of lowering the battery resistance and the effect of lowering the restraining pressure. You may.

In the present disclosure, the porosity in the negative electrode layer is a value calculated from the negative electrode layer in a state after the initial discharge of the all-solid-state battery. The initial discharge means the first discharge of the all-solid-state battery after the all-solid-state battery is assembled and the all-solid-state battery is charged for the first time. Further, in the present disclosure, since the negative electrode layer does not include the negative electrode current collector, the volume of the negative electrode current collector does not affect the porosity of the negative electrode layer.
The method for calculating the porosity is not particularly limited, but can be calculated using, for example, "3D-SEM".
Specifically, it is a photograph of the laminated cross section of the all-solid-state battery viewed from the front with respect to the all-solid-state battery after the initial discharge, and is a photograph of the surface portion of the negative electrode layer of the all-solid-state battery (for example, 5 μm × 5 μm size). Photo). Then, the surface of the negative electrode layer is irradiated with an ion beam, the surface of the negative electrode layer is excavated, and the surface of the negative electrode layer is photographed again. The excavation of the surface of the negative electrode layer and the photographing of the surface of the negative electrode layer by the ion beam irradiation are repeated to obtain a 2D photograph group of the surface of the negative electrode layer. Then, each 2D region of the obtained group of 2D photographs is discriminated, the area of the void existing in the 2D region is calculated, and the area is integrated to calculate the volume of the void in the 3D region. Then, the porosity can be calculated by calculating the volume of the void with respect to the volume of the entire 3D region.

Examples of the conductive material include carbon materials such as acetylene black and Ketjen black, fibrous carbon such as carbon fiber, and metal materials, which are preferable from the viewpoint of improving contact between particles. It may be fibrous carbon.
The content of the conductive material in the negative electrode layer is not particularly limited, but may be 0% by volume to 16% by volume, for example, when the total volume of the negative electrode layer is 100% by volume.
The binder is not particularly limited, and examples thereof include butadiene rubber (BR), polyvinylidene fluoride (PVdF), and styrene-butadiene rubber (SBR).
The content of the binder in the negative electrode layer is not particularly limited, but may be 0.5% by volume to 10% by volume, for example, when the total volume of the negative electrode layer is 100% by volume.
The thickness of the negative electrode layer is not particularly limited, but may be, for example, 10 to 100 μm, preferably 10 to 50 μm.

The method for producing the negative electrode layer is not particularly limited, and examples thereof include the following methods.
First, a negative electrode active material and a solid electrolyte are prepared.
Then, the negative electrode active material and the solid electrolyte are mixed to obtain a mixture.
The mixture is pressed and molded to obtain a molded body. The press pressure here is not particularly limited, and may be, for example, 0.7 to 1.4 ton / cm ² (≈68.6 to 137.2 MPa).
Then, a solution prepared by dissolving the solid electrolyte in an organic solvent is applied to the surface of the molded body, and the solution is permeated into the molded body.
Then, the solution in the molded body is dried to obtain a negative electrode mixture.
The content of the solid electrolyte in the solution is not particularly limited, but may be 2.4 to 10% by mass. The organic solvent may be any solvent as long as the solid electrolyte is soluble and volatile, and examples thereof include ethanol.
Then, the negative electrode mixture is pressed to obtain a negative electrode layer having desired voids. The press pressure here is not particularly limited, and may be, for example, 0.7 to 1.4 ton / cm ² (≈68.6 to 137.2 MPa).
The negative electrode layer is preferably manufactured in an atmosphere of an inert gas such as argon gas.

The porosity between the electrolytes in the negative electrode layer is adjusted by the press pressure applied to the negative electrode mixture when forming the negative electrode layer, the content of the solid electrolyte contained in the solution permeated from the surface of the molded body, and the like. be able to.
By pouring a solution in which a solid electrolyte is dissolved using a volatile organic solvent such as ethanol into the molded body, the volume of the molded body is increased by the volume of the solution. Then, it is presumed that the organic solvent contained in the molded product dries and evaporates to form a solid electrolyte region having a desired space between electrolytes.

The negative electrode current collector has a function of collecting current in the negative electrode layer.
Examples of the material of the negative electrode current collector include metal materials such as SUS, Ni, Cr, Au, Pt, Al, Fe, Ti, Zn, and Cu.
Moreover, as the shape of the negative electrode current collector, for example, a foil shape, a plate shape, a mesh shape and the like can be mentioned.
The negative electrode may further include a negative electrode lead connected to the negative electrode current collector.

The positive electrode has at least a positive electrode layer, and if necessary, further includes a positive electrode current collector.
The positive electrode layer contains at least a positive electrode active material, and if necessary, a conductive material, a binder, and a solid electrolyte.
Conventionally known materials can be used as the positive electrode active material. When the all-solid-state battery is a lithium battery, examples thereof include lithium single metal, lithium alloy and lithium-containing metal oxide. As the lithium alloy, for example, an In-Li alloy or the like can be used. Examples of the lithium-containing metal oxide include rock salt layered active materials _{such as LiCoO 2} , LiNiO ₂ , LiVO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O _{2 , LiMn 2} O ₄ , Li (Ni _{0). .5} Mn _1.5) spinel active material _{O 4} or the _like, can be cited LiFePO _4, LiMnPO _4, LiNiPO 4, LiCoPO olivine active material such as _4.
The shape of the positive electrode active material is not particularly limited, and examples thereof include a particle shape and a plate shape.
The positive electrode active material may have a coating layer in which the surface of the positive electrode active material is coated with a solid electrolyte.
Method of coating the surface of the positive electrode active material in the solid electrolyte is not particularly limited, for example, by using tumbling fluidized coating apparatus (manufactured by Powrex Corp.), a solid electrolyte ₃ such as LiNbO the positive electrode active material in the atmospheric environment Examples thereof include a method of coating and firing in an air environment. Further, for example, a sputtering method, a sol-gel method, an electrostatic spraying method, a ball milling method and the like can be mentioned.
The solid electrolyte that forms the coating layer may be a substance that has lithium ion conductivity, does not flow even when in contact with an active material or a solid electrolyte, and can maintain the morphology of the coating layer, for example. , LiNbO ₃ , Li ₄ Ti ₅ O ₁₂ , Li ₃ PO _{4, and the} like.
In addition, as the solid electrolyte used for the positive electrode layer, the same solid electrolyte as that used for the solid electrolyte layer described later can be used.
As the conductive material and the binder used for the positive electrode layer, the same ones as those used for the negative electrode layer can be used.
The thickness of the positive electrode layer is not particularly limited, but may be, for example, 10 to 250 μm, particularly 20 to 200 μm.
The content of the positive electrode active material in the positive electrode layer is not particularly limited, but may be, for example, 50% by volume to 100% by volume when the total volume of the positive electrode layer is 100% by volume.
The method for forming the positive electrode layer is not particularly limited, and examples thereof include a method of pressure molding a powder of a positive electrode material containing a positive electrode active material and, if necessary, other components.

The positive electrode current collector has a function of collecting current in the positive electrode layer.
As the material of the positive electrode current collector, the same material as that of the negative electrode current collector can be adopted.
Further, as the shape of the positive electrode current collector, the same shape as that of the negative electrode current collector can be adopted.
The positive electrode may further include a positive electrode lead connected to the positive electrode current collector.

The solid electrolyte layer contains at least a solid electrolyte, and may contain a binder or the like, if necessary.
Examples of the solid electrolyte used in the solid electrolyte layer include oxide-based solid electrolytes and sulfide-based solid electrolytes having high Li ion conductivity, and sulfide-based solid electrolytes are preferable.
As the sulfide-based solid electrolyte, the same one as that used for the negative electrode layer can be used.
Examples of the oxide-based solid electrolyte include Li _6.25 La ₃ Zr ₂ Al _0.25 O ₁₂ , Li ₃ PO ₄ , Li _{3 + x} PO _4-x N _x (LiPON), and the like. Examples of the electrolyte include Li ₇ P ₃ S ₁₁ , Li ₃ PS ₄ , Li ₈ P ₂ S ₉ , Li ₁₃ GeP ₃ S ₁₆ , Li ₁₀ GeP ₂ S _{12, and the} like.
As the solid electrolyte, one kind alone or two or more kinds can be used. When two or more kinds of solid electrolytes are used, two or more kinds of solid electrolytes may be mixed, or two or more layers of each solid electrolyte may be formed to form a multilayer structure.
The ratio of the solid electrolyte in the solid electrolyte layer is not particularly limited, but may be, for example, 50% by mass or more, 60% by mass or more and 100% by mass or less, and 70% by mass or more and 100% by mass. It may be in the range of mass% or less, or may be 100 mass%.

Examples of the method for forming the solid electrolyte layer include a method of pressure molding a powder of a solid electrolyte material containing a solid electrolyte and, if necessary, other components. When the powder of the solid electrolyte material is pressure-molded, a press pressure of about 1 MPa or more and 400 MPa or less is usually applied.
As the binder used for the solid electrolyte layer, the same binder as that used for the negative electrode layer described above can be used.
The thickness of the solid electrolyte layer is usually about 0.1 μm or more and 1 mm or less.

The all-solid-state battery in the present disclosure is a concept including a state after the initial discharge.
The all-solid-state battery includes, if necessary, a positive electrode, a negative electrode, and an exterior body that houses the solid electrolyte layer.
The shape of the exterior body is not particularly limited, and examples thereof include a laminated type.
The material of the exterior body is not particularly limited as long as it is stable to the electrolyte, and examples thereof include resins such as polypropylene, polyethylene, and acrylic resin.

Examples of the all-solid-state battery include a lithium battery, a sodium battery, a magnesium battery, a calcium battery, and the like, and a lithium battery may be preferable.
Examples of the shape of the all-solid-state battery include a coin type, a laminated type, a cylindrical type, and a square type.

The method for producing the all-solid-state battery of the present disclosure is not particularly limited, and the all-solid-state battery can be produced by a conventionally known method.
For example, a solid electrolyte layer is formed by pressure molding a powder of a solid electrolyte material containing a solid electrolyte. Then, the negative electrode layer is obtained by carrying out the above-mentioned manufacturing method of the negative electrode layer on one surface of the solid electrolyte layer. Then, the positive electrode layer is obtained by pressure molding the powder of the positive electrode material on the surface of the solid electrolyte layer opposite to the surface on which the negative electrode layer is formed. Then, an all-solid-state battery can be manufactured by first charging and discharging the obtained positive electrode layer-solid electrolyte layer-negative electrode layer conjugate.
In this case, the press pressure for pressure molding the powder of the solid electrolyte material and the powder of the material for the positive electrode is usually about 1 MPa or more and 600 MPa or less.
The pressurizing method is not particularly limited, and examples thereof include a method of applying pressure using a flat plate press, a roll press, or the like.

(Sulfide-based solid electrolyte synthesis)
In a glove box under an argon atmosphere _{, weigh 0.7656 g of Li 2} S and 1.2344 g of P ₂ S _{5 using Li 2} S (Nippon Kagaku Kogyo) and P ₂ S ₅ (Aldrich) as starting materials, and weigh agate. The mixture was mixed in a mortar for 5 minutes, and then 4 g of heptane was added to obtain a raw material composition. Next, 1 g of the raw material composition was placed in a zirconia pot (45 ml) together with zirconia balls (5 mmφ, 80 pieces), and the pot was completely sealed (argon atmosphere). This pot was attached to a planetary ball mill (P7 manufactured by Fritsch Japan Co., Ltd.), and mechanical milling was performed at a base rotation speed of 500 rpm for 40 hours to obtain a powder _{of Li 8} P ₂ S _{9 as a sulfide-based solid electrolyte.}

(Example 1)
[Positive electrode mixture]
As the positive electrode active material, lithium nickel cobalt manganate LiNi _3/5 Co _1/5 Mn _1/5 O ₂ was used. The positive electrode active material was surface-treated with _{LiNbO 3.} Weigh 12.5 mg of the positive electrode active material, 0.460 mg of VGCF (registered trademark, manufactured by Showa Denko) as a conductive material, and 3.53 mg of Li ₈ P ₂ S ₉ as a solid electrolyte, and mix them to make a positive electrode. It was made into a mixture.
[Negative electrode mixture]
Organic with 2.45 mg of silicon powder as the negative electrode active material _{, 1.80 mg of Li 8} P ₂ S ₉ as the solid electrolyte, 0.18 mg of VGCF as the conductive material, and a binder containing 75 mol% of PVdF at a concentration of 5% by mass. It was dissolved in a solvent, and 1.6 mg of the dissolved product was mixed with the mixture to obtain a mixture.
Then, the above mixture was smoothly ^{packed in a 1 cm 2 ceramic mold and press-molded at 0.5 ton / cm 2} (≈49 MPa) to obtain a molded product.
After removing the obtained molded product from the mold, a solid electrolyte _{prepared by dissolving Li 8} P ₂ S ₉ in ethanol at a ratio of 6.0% by mass was applied onto the surface of the molded product. Then, it was dried at room temperature for 1 hour to prepare a negative electrode mixture.
[All-solid-state battery]
As a solid electrolyte, 15 mg of _{Li 8} P ₂ S ₉ ^{was weighed in a 1 cm 2} ceramic mold and ^{pressed at 1 ton / cm 2} (≈98 MPa) to prepare a solid electrolyte layer.
The positive electrode mixture prepared above was placed on one surface of the solid electrolyte layer ^{and pressed at 1 ton / cm 2} (≈98 MPa) to prepare a positive electrode layer. Further, an aluminum foil was used for the positive electrode current collector, and the positive electrode current collector was arranged on the surface of the positive electrode layer opposite to the surface on which the solid electrolyte layer was formed to form a positive electrode.
The negative electrode mixture prepared above was placed on the other surface of the solid electrolyte layer ^{and pressed at 1.3 ton / cm 2} (≈127.4 MPa) to prepare a negative electrode layer. Further, a copper foil was used for the negative electrode current collector, and the negative electrode current collector was arranged on the surface of the negative electrode layer opposite to the surface on which the solid electrolyte layer was formed to serve as the negative electrode.
An all-solid-state battery was obtained by the above procedure.

(Examples 2 to 8 and Comparative Examples 1 to 6)
In the above [negative electrode mixture], the content of the solid electrolyte in ethanol when the surface of the molded body is coated, and in the above [all-solid-state battery], the press pressure applied to the negative electrode mixture at the time of producing the negative electrode layer. An all-solid-state battery was obtained in the same manner as in Example 1 except that the changes were made as described in Table 1.

[Charge / discharge test]
A charge / discharge test was performed using the all-solid-state batteries obtained in Examples 1 to 8 and Comparative Examples 1 to 6.
The obtained all-solid-state battery was evaluated by a restraint jig under a restraint pressure of 0.8 MPa.
Initial charge: CC / CV was charged to 4.35V at 0.3mA.
The highest value of the pressure increase at that time was used for the effect measurement.
Initial discharge: After the initial charge, CC / CV discharge was performed at 0.5 mA to 2.5 V.
[Pressure value]
The restraint pressure was adjusted by sandwiching the load cell between the restraint plates.
The pressure increase during charging was measured through the load cell.
Tables 1 to 3 show the relative pressures of Examples 1 to 8 and Comparative Examples 1 to 6 when charging with Example 2 as the reference value 100.
After that, DC-IR measurement was performed.
[Resistance value]
DC-IR measurement: The resistance value was obtained from the voltage drop when a current of 8.5 mA was passed for 5 seconds after adjusting the voltage to 3.5 V.
Tables 1 to 3 show the relative resistance values of Examples 1 to 8 and Comparative Examples 1 to 6 with Example 2 as the reference value 100.

[Porosity]
The total porosity in the negative electrode layer, the porosity between the electrolytes in the solid electrolyte region, and the porosity between the electrolytes in the negative electrode layer were determined by 3D-SEM.
3D-SEM: A planar SEM image was measured in a minute region of 5 μm × 5 μm for the negative electrode layer portion of the all-solid-state battery. After that, the minute region on the surface of the negative electrode layer is excavated by irradiating an ion beam, and the method of measuring and observing a flat SEM image in the minute region is repeated, and the depth of the minute region on the surface of the negative electrode layer is 5 μm. The plane SEM image was measured up to the region.
After that, the area of the void in each plane SEM image was calculated, and the area was integrated to calculate the volume of the void occupied in the minute region.
Then, the porosity was calculated from the volume of the void with respect to the volume of the entire minute region.
The results are shown in Tables 1-3.

[Charge / discharge test results]
As shown in Table 1, in Examples 1 to 8 and Comparative Examples 1 to 6, it can be seen that Examples 1 to 8 have lower relative resistance values than Comparative Examples 1 to 6. Therefore, when the porosity between the electrolytes in the negative electrode layer is in the range of 3.4 to 29.6% by volume, the effect of reducing the binding pressure of the battery and the effect of reducing the resistance value of the battery are recognized, and the effect of reducing the binding pressure of the battery and the battery It can be seen that the balance of the resistance value reduction effect of is good.
Further, in Example 2 and Comparative Examples 1 to 6, it can be seen that Comparative Examples 1 to 6 have higher relative resistance values than Example 2, and the balance between the effect of reducing the restraining pressure of the battery and the effect of reducing the resistance value of the battery is poor. ..
Further, from the results of Comparative Examples 2 to 5, the porosity between the electrolytes in the negative electrode layer was controlled to a low value of 0.9 to 2.3% by volume, and the total porosity in the negative electrode layer was controlled from 3% by volume to 45% by volume. When the total porosity in the negative electrode layer is increased to, the restraining pressure of the battery tends to decrease as the total porosity in the negative electrode layer increases, but the resistance value of the battery may increase when the total porosity in the negative electrode layer exceeds 40% by volume. Understand.
Further, from the results of Comparative Example 1, since Comparative Example 1 has an extremely high relative pressure and relative resistance value as compared with Example 2, even if the total porosity in the negative electrode layer is 10 to 15% by volume, the electrolyte in the negative electrode layer. It can be seen that when the porosity is as small as 0.2% by volume, the effect of reducing the restraining pressure of the battery and the effect of reducing the resistance value of the battery cannot be obtained. Therefore, it can be seen that the effect of reducing the confining pressure of the battery and the effect of reducing the resistance value of the battery cannot be obtained simply by setting the total porosity in the negative electrode layer to 10 to 15% by volume.

As shown in Table 2, from the results of Examples 2 to 5 and Comparative Example 5, the total porosity in the negative electrode layer was controlled to 15% by volume, and the porosity between the electrolytes in the negative electrode layer was 2.3% by volume (Comparative Example). 5), 6.0% by volume (Example 2), 8.3% by volume (Example 3), 9.8% by volume (Example 4), 12.0% by volume (Example 5). As a result, it was confirmed that the balance between the effect of reducing the restraining pressure of the battery and the effect of reducing the resistance value of the battery became better. Therefore, when the void ratio between the electrolytes in the negative electrode layer is within the range of 6.0 to 12.0% by volume, the expansion of the negative electrode active material during battery charging can be easily absorbed, and the negative electrode active material and the solid electrolyte can be used. It is presumed that the contact property at the interface between the two is improved.
Similarly, from the results of Examples 2 to 5 and Comparative Example 5, the total porosity in the negative electrode layer was controlled to 15% by volume, and the porosity between the electrolytes in the solid electrolyte region was 15% by volume (Comparative Example 5), 40 volumes. % (Example 2), 55% by volume (Example 3), 65% by volume (Example 4), 80% by volume (Example 5). It was confirmed that the balance of the value reduction effect became better. Therefore, it was confirmed that when the porosity between the electrolytes in the solid electrolyte region is within the range of 40 to 80% by volume, the balance between the effect of reducing the restraining pressure of the battery and the effect of reducing the resistance value of the battery is excellent.

Further, from the results of Examples 6 to 8, the total porosity in the negative electrode layer was controlled to 38%, and the porosity between the electrolytes in the negative electrode layer was 19.8% by volume (Example 6) and 25.8% by volume (Example). It was confirmed that by increasing the volume to 29.6% by volume (Example 7) and 29.6% by volume (Example 8), the balance between the effect of reducing the restraining pressure of the battery and the effect of reducing the resistance value of the battery was improved. Therefore, it was confirmed that when the porosity between the electrolytes in the negative electrode layer is in the range of 19.8 to 29.6% by volume, the balance between the effect of reducing the restraining pressure of the battery and the effect of reducing the resistance value of the battery is excellent. ..

As shown in Table 3, from the results of Examples 1, 4 and 7, and Comparative Examples 4 and 6, the porosity between the electrolytes in the solid electrolyte region was controlled in the range of 65 to 70% by volume, and the total porosity in the negative electrode layer was controlled. The rate is increased to 3% by volume (Comparative Example 4), 5% by volume (Example 1), 15% by volume (Example 4), 38% by volume (Example 7), and 45% by volume (Comparative Example 6). As a result, it was confirmed that when the total porosity in the negative electrode layer is in the range of 5% by volume to 38% by volume, the balance between the effect of reducing the restraining pressure of the battery and the effect of reducing the resistance value of the battery is excellent.
Similarly, from the results of Examples 1, 4 and 7, and Comparative Examples 4 and 6, the porosity between the electrolytes in the solid electrolyte region was controlled in the range of 65 to 70% by volume, and the porosity between the electrolytes in the negative electrode layer was set to 2. .1% by volume (Comparative Example 4), 3.4% by volume (Example 1), 9.8% by volume (Example 4), 25.8% by volume (Example 7), 31.1% by volume (Comparison) By increasing with Example 6), if the porosity between the electrolytes in the negative electrode layer is in the range of 3.4 to 25.8% by volume, the balance between the effect of reducing the restraining pressure of the battery and the effect of reducing the resistance value of the battery is excellent. I was able to confirm that.

From the above results, the all-solid-state battery provided with the negative electrode layer in which the porosity between the electrolytes in the negative electrode layer is in the range of 3.4 to 29.6% by volume has the effect of reducing the restraining pressure of the battery and the effect of reducing the resistance value of the battery. It proved to be well-balanced.

11 Solid electrolyte layer 12 Positive electrode layer 13 Negative electrode layer 14 Positive electrode current collector 15 Negative electrode current collector 16 Positive electrode 17 Negative electrode 21 Solid electrolyte particles 22 Negative electrode active material particles 23 Solid electrolyte region 24 Electrode gap 25 Negative electrode active material-Solid electrolyte gap 100 all-solid-state battery

Claims (4)

An all-solid-state battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer arranged between the positive electrode layer and the negative electrode layer.
The negative electrode layer contains a negative electrode active material containing at least one Si-based material selected from the group consisting of Si and a Si alloy, and a solid electrolyte containing a sulfide-based solid electrolyte.
In the negative electrode layer, there is an inter-electrolyte void surrounded by the solid electrolyte, at least in a region composed of the solid electrolyte.
When the total volume of the negative electrode layer is 100% by volume, the porosity occupied by the interelectrolyte voids in the negative electrode layer is 3.4% by volume or more and 29.6% by volume or less. battery. The all-solid-state battery according to claim 1, wherein the negative electrode layer further contains fibrous carbon as a conductive material. Claim 1 or 2 in which, when the total volume of the negative electrode layer is 100% by volume, the porosity occupied by all the voids existing in the negative electrode layer of the negative electrode layer is 5% by volume or more and 38% by volume or less. All-solid-state battery described in. The claim that the porosity occupied by the interelectrolyte voids in the region is 40% by volume or more and 80% by volume or less, assuming that the total volume of the region composed of the solid electrolyte in the negative electrode layer is 100% by volume. The all-solid-state battery according to any one of 1 to 3.

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